1. Field of the Invention
This invention relates generally to a dual magnetic drive for use in a gear meter. More particularly, this invention concerns the use of magnets in both measuring gears of a gear meter to drive two shafts, the torque outputs of which are operatively coupled by two gears outside the measuring chamber of the meter.
2. Description of the Prior Art
It has been common in the past to use magnetic drives in industrial meters. Such arrangements are preferred over shaft drives requiring dynamic seals. Gear-type meters lend themselves to the use of magnetic drives because it is possible to put a driver magnet in a measuring gear and a driven magnet on a rotating shaft inside a fixed hollow shaft on which the measuring gear rotates. However, previous designs have used only a single magnetic coupling in such meters. The meters described at page 3 of Catalog No. M-1002, 1966, of Oval Gear Engineering Co., Ltd., are believed exemplary of such a single magnetic coupling. While this arrangement has exhibited at least a degree of utility in larger meters, it is believed that room for significant improvement remains.
Generally, a single magnetic drive has been adequate in meters where the components are large enough that they can generate sufficient torque through the magnetic drive to operate meter accessories such as a volume indicator, a preset counter, or a pulse transmitter. However, as the need for, and the use of smaller meters has developed, the parts or components thereof have also become smaller. The result has been that a point is reached where the torque produced by a single magnetic drive is not sufficient to operate the same meter accessories previously driven on larger meters.
In the past, as gear meters were made smaller, one of the following results occurred. First, fewer or no mechanical accessories were driven by the meter. In these situations, it was necessary to resort, for example, to the use of electrical signals to record rotations of the measuring gears in order to calculate the volume of fluid passing through the meter. Alternatively, larger magnetic drives were used. However, these drives have been located outside of the measuring gear in order not to have to reduce the accessory load that the meter can operate. This approach required that more parts be used, and, in some cases, that more parts be subjected to the measured fluid. For example, attention is directed to U.S. Pat. Nos. 3,255,630 (Karlby) and 3,448,615 (Schneider) which appear to disclose single magnetic drives located outside the measuring chambers. The consequence is an increased complexity and cost. Furthermore, the consequences are the same whether the larger driver magnet is attached directly to the measuring gear or is indirectly driven by the measuring gear.
In most instances, the measuring gears or rotors used in meters for measuring the flow of fluids are bilobar or oval shaped bodies such as described in U.S. Pat. No. 2,368,019 (Guibert). These rotors are caused to be rotated about their axes by the passage of the fluid through the measuring chamber. Magnetic coupling has been utilized wherein one of the rotors, rotating about a hollow shaft, is used to magnetically drive another shaft arranged within the hollow shaft. However, because of the shape and alignment of the rotors within the measuring chamber, the speed of each of the measuring rotors varies during each 360 degree rotation. Due to this variation in speeds of the measuring rotors, utilization of both rotors to drive "accessory" shafts did not appear feasible such that an increased "accessory torque" (over that produced by a single rotor drive) could be generated. Consequently, the use of a dual magnetic drive, that is, the use of a driving magnet in each of the measuring rotors, required the development of an arrangement which would make the torques produced by the two rotors of varying angular acceleration additive, and not counter-productive. This problem is believed to have been solved by the invention described herein.
The problems enumerated in the foregoing are not intended to be exhaustive but rather are believed to be among many which may tend to impair the effectiveness of previously known gear meters. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that the gear meter systems which appear in the art have not been altogether satisfactory as the need to use smaller gear meters has developed.
Recognizing the need for an improved arrangement for driving gear meter accessories, it would be advantageous to provide a dual magnetic drive for gear meters which minimizes or reduces the problems of the type previously noted. More particularly, it would be advantageous to be able to increase the amount of torque that can be transmitted by magnetic drives in a gear meter such that smaller gear meters may drive the same meter accessories previously driven by larger meters. Another advantage to be achieved is increased economy and efficiency in gear meters where fewer parts and mechanisms are needed and where fewer parts are subjected to the measured fluid such that measuring accuracy is not hindered or reduced.